Liquid toner development

ABSTRACT

In developing an electrostatic latent-image-bearing surface with a liquid developer containing a highly volatile liquid component, a thin layer of residual liquid developer is formed on the surface. This thin residual developer layer is substantially removed by subjecting the layer to a stream of gas containing a relatively large quantity of the vapor of the highly volatile liquid component. Toner background deposit and image quality is improved with this technique.

I United States Patent Inventor Seiji Matsumoto c/o Fuji Photo Film Co., Ltd. No. 105, One Mizonuma, Asaka-shi Saitama-ken, Asaka, Japan Appl. No. 43,466

Filed June 4, 1970 Patented Dec. 21, 1971 Priority June 9, 1969 Japan #4/45269 LIQUID TONER DEVELOPMENT 6 Claims, 1 Drawing Fig.

US. Cl 117/37 LX, 252/62.l,96/l R Int. Cl B05c 1/16, 603g 9/00 Field of Search 252/621;

[56] References Cited UNITED STATES PATENTS 3,356,498 l2/l967 Moe et al 96/! 3,382,763 5/l968 Bruning 88/24 3,498,917 3/1970 Witter 252/621 Primary Examiner-George F. Lesmes Assistant Examiner-M. B. Wittenberg Attorneys- Paul M. Enlow, James J. Ralabate, Albert A.

Mahassel and Peter H. Kondo ABSTRACT: In developing an electrostatic latent-imagebearing surface with a liquid developer containing a highly volatile liquid component, a thin layer of residual liquid developer is formed on the surface. This thin residual developer layer is substantially removed by subjecting the layer to a stream of gas containing a relatively large quantity of the vapor of the highly volatile liquid component. Toner background deposit and image quality is improved with this technique.

FATENTEB HEEZH m M INVENTOR. SEMI WTSUMOTO flTTOR/VEY BACKGROUND OF THE INVENTION This invention relates to imaging systems, and more particularly, to improved processes for treating electrostatographic imaging surfaces developed with liquid developers.

The formation and development of images on a surface of photoconductive materials by electrostatic means is well known. One conventional process involves placing a uniform electrostatic charge on a photoconductive insulating layer comprising zinc oxide powder and a resinous binder carrier on a conductive paper substrate, exposing the layer to a lightand-shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting electrostatic latent image by depositing on the image a charged toner which is dispersed in an insulating carrier liquid. The charged toner may be suitably colored and may have a polarity of charge identical or opposite to that of the latent image to be developed. If the polarity of the charge of the toner is identical to that of the latent image, reversal development will occur whereas a toner having a charge opposite of that of the latent image will be attracted to the latent image.

Since development is normally effected by immersion of the imaging surface in a developer bath, a thin layer of developer liquid remains on the imaged surface upon removal of the imaged surface from the developer bath. If the thin layer of developer liquid is not returned to the bath, consumption of the liquid developer will be high. If the thin layer of developer liquid is allowed to dry on the imaged surface, excess toner material will remain on the background areas of the imaged surface and the images will exhibit a tendency to smear. Thus, an additional cleaning step is required to reduce the effects of permitting the thin layer of developer liquid to dry on the imaged surface. If the thin layer of liquid developer is allowed to dry completely, considerable difficulty is experienced in improving the quality of the imaged surface with a cleaning step. The thin layer of liquid developer may be removed with a squeeze roller. Unfortunately, this treatment with a squeeze roller tends to smear the imaged surface. Removal of the thin layer of liquid developer may be accomplished by directing a rapidly moving stream of air against the imaged surface. However, since carrier liquids generally contain a highly volatile component, the stream of air rapidly vaporizes the volatile component and causes fluctuations in the density of the images. Thus, there is a continuing need for an improved imaging system.

SUMMARY OF THE INVENTION It is therefore, and object of this invention to provide an imaging system overcoming the above-noted deficiencies.

It is another object of this invention to provide an imaging system which improves electrostatographic image quality.

It is a further object of this invention to provide an imaging system which forms images having more uniform density.

It is still another object of this invention to provide an imaging system having reduced background deposits.

It is another object of this invention to provide an imaging system superior to those of known imaging systems.

The above objects and others are accomplished, generally speaking, by providing an imaging member having a recording surface bearing an electrostatic latent image, developing the latent image with a liquid developer containing a highly volatile liquid component to form an imaged recording surface having a thin layer of developer liquid thereon, and directing a stream of gas containing a relatively large quantity of the vapor of the volatile liquid component against the imaged recording surface thereby removing the thin layer of developer liquid by a squeezing action. The vapor pressure of the vapor in the gas should be substantially equal to the saturated vapor pressure of the volatile liquid at the temperature at which the gas is employed. The high concentration of vapor in the gas stream permits removal of the thin layer of developer liquid on the imaged surface and return of this removed liquid developer to the developer bath without undue loss of the volatile liquid component of the liquid developer. in addition, the high vapor content of the stream of gas prevents fluctuations in the image density to occur on the imaged surface during the squeezing operation.

BRIEF DESCRIPTION OF THE DRAWING The advantages of the improved electrostatographic imaging system of this invention will become even further apparent upon consideration of the following disclosure of the invention, particularly when taken in conjunction with the accompanying drawing illustrating a schematic sectional view of an electrostatographic development and doctoring apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The carrier liquids employed in the liquid developers of this invention comprise liquid components having low volatility mixed in suitable ratios with liquid components having high volatility to pennit normal handling in conventional liquid development electrostatographic machines. Any suitable highly volatile liquid may be employed as the highly volatile liquid component in the carrier liquid of this invention. Typical highly volatile liquids include cyclohexane, carbon tetrachloride, n-hexane, fluorinated hydrocarbons such as 1,1,2-trichloro-l,2,2trifluoroethylene, and the like. The expression "highly volatile is intended to include liquids having a boiling point between about and about 200 F. The liquid developer component having a high degree of volatility is used in the developer to dissolve the conventional resinous component of the liquid developer and to promote rapid drying of the imaged recording member. Any suitable low volatility liquid may be employed in the liquid developers of this invention. Typical low volatility liquids include high boiling point petroleum fractions such as kerosene, isoparaffins and the like. The expression low volatility is intended to include liquids having a boiling point greater than about 250 F. The high boiling point liquid is employed in liquid developers to facilitate handling and to insure stability for long periods of time. Liquid developers containing one or more of the above described components are well known in the prior art. Generally, for practical drying speeds, at least about 5 percent highly volatile liquid based on the total weight of carrier liquid is preferred.

For optimum removal of the thin layer of liquid developer from the imaged surface with the gas stream of this invention, the vapor pressure of the highly volatile liquid component of the carrier liquid should be close to its saturated vapor pressure at the average operating temperature of the gas stream. Satisfactory results are achieved with gas-stream temperatures below about the boiling point of said highly volatile carrier liquid component. The high concentration of vapor in the one or more streams of gas employed in this invention prevents abrupt evaporation of the highly volatile component of the liquid developer thereby preventing degradation of image quality. The high concentration of vapor in the gas stream also permits recovery and reuse of the liquid developer removed from the imaged surface without significant changes in the relative concentration of the highly volatile liquid in the recovered liquid developer. If the vapors used in the gas stream are flammable, the concentration of the vapors should exceed the upper explosion limit. More preferably, the flammable vapor may be admixed with inert gases such as nitrogen, carbon dioxide or vapors of nonflammable solvents containing a halogen. Obviously, in continuous processes where air from the ambient atmosphere becomes admixed with the gas stream, continuous introduction of a predetermined amount of inert gases or vapors will reduce the danger of explosions. Alternatively, the apparatus employed to carry out the process of this invention may be airtight and the internal pressure may be maintained slightly higher than the external pressure. The velocity of the gas stream should be sufi'lcient to cause the: developer liquid in the thin residual layer to visibly flow away from the point of impact of the gas stream on the imaged recording surface.

Referring now to the drawing, a recording element I carrying an electrostatic latent image on the upper surface is conveyed in the direction indicated by the arrow. A container 2 of developer liquid 3 is positioned below the path of travel of recording element l. The developer liquid 3 is fed by pump 4 into developing head 5. The developing liquid supplied by developing head .5 contacts and develops the electrostatic latent image carried on the upper surface of recording element 1 supported by an electrically grounded conductive support member 14. Although some of the excess developer liquid 3 flows over the edges of recording element 1 into container 2, some of the developer liquid remains deposited as a thin layer on the upper surface of recording element 1. This thin layer of developer liquid is subjected to at least one gas stream supplied by nozzle 6. The gas for the gas stream supplied by nozzle 6 is drawn into the ducts 7 and 7' from the area immediately adjacent to the exit opening of nozzle 6 and is delivered to 1101.118 6 by means of fan 8. Recording element 1 is supported by roller 9 positioned immediately below the exit opening of nozzle 6. The strong stream of gas emitted from nozzle 6 presses recording element 1 against roller 9 and removes the thin layer of liquid developer on the upper surface of recording element 1 by a squeezing action thereby causing the developer liquid to flow over both edges of recording element 1 back. into container 2. At the same time, a portion of the highly volatile component of the carrier liquid is vaporized. Since most of the stream of gas supplied by nozzle 6 is drawn into ducts 7 and 7 and recycled by fan 8, abrupt vaporization of the carrier liquid in the thin film of developer liquid on the surface of recording element 1 is avoided thereby promoting the formation of high-quality images and prevent ing substantial changes in component concentration of the recovered developer liquid, After the gas-stream squeezing operation, recording element 1 is transported over a container 10 of cleaning liquid ll. Cleaning liquid 11 is pumped by means of pump 13 to cleaning head 12 located over the upper surface of recording element 1. The cleaning liquids supplied to the upper surface of the recording element l by cleaning head 12 reduces background toner deposits and decreases the tendency of the images to smear. Since background deposits are markedly reduced as a result of removal of substantially all of the developing liquid from the upper surface of recording element 1 by means of the air squeezing action, the subsequent treatment of recording element 1 with cleaning liquid 11 is optional. Generally, the cleaning operation is employed where images or extremely high quality are required. It is apparent that the removal of the thin layer of liquid developer after development from the upper surface of the recording element 1 by the air squeezing treatment greatly reduces the rate of contamination of cleaning liquid 11 with liquid developer materials carried over on the surface of recording element 1 from the development operation. Thus, in automatic machines in which the cleaning liquid is recycled, the useful life of the cleaning liquid is lengthened considerably.

Although specific materials and conditions are set forth in the foregoing examples, these are merely intended as illustra tions of the present invention. Various other suitable carrier liquid components, toners, developer additives and gaseous materials for the gas stream may be employed to sensitize, synergize or otherwise improve the imaging properties or other properties of the system. Also, conventional techniques to charge and develop the electrostatographic insulating layer may be employed, including for example, the well-known double corona charging technique Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is: I I I, An imaging process comprising providing an electrostatic latent-image-bearing surface, contacting said electrostatic latent-image-bearing surface with a liquid developer comprising toner particles and carrier liquid, said carrier liquid comprising at least one highly volatile liquid whereby a thin layer of residual liquid developer adheres to said electrostatic latent-image-bearing surface and at least a portion of said toner particles deposits on said electrostatic latent-imagebearing surface in image configuration, and directing a stream of gas against said thin layer to remove said residual liquid developer from said electrostatic latent-image-bearing surface, said gas comprising a vapor of said highly volatile liquid at a vapor pressure substantially equal to the saturated vapor pressure of said vapor at the average temperature of said gas stream.

2. An imaging process according to claim 1 wherein said carrier liquid comprises at least one highly volatile liquid and at least one liquid having low volatility.

3. An imaging process according to claim 1 including recycling said gas containing said vapor of said highly volatile liquid and removing residual liquid developer from additional image bearing surfaces.

4. An imaging process according to claim 1 including collecting said residual liquid developer removed by said gas stream and reusing said residual liquid developer to develop additional electrostatic latent-image-bearing surfaces.

5. An imaging process according to claim 1 wherein said highly volatile liquid has a boiling point between about F. and about 200 F.

6. An imaging process according to claim 2 wherein said liquid having low volatility has a boiling point greater than about 250 F. 

2. An imaging process according to claim 1 wherein said carrier liquid comprises at least one highly volatile liquid and at least one liquid having low volatility.
 3. An imaging process according to claim 1 including recycling said gas containing said vapor of said highly volatile liquid and removing residual liquid developer from additional image bearing surfaces.
 4. An imaging process according to claim 1 including collecting said residual liquid developer removed by said gas stream and reusing said residual liquid developer to develop additional electrostatic latent-image-bearing surfaces.
 5. An imaging process according to claim 1 wherein said highly volatile liquid has a boiling point between about 100* F. and about 200* F.
 6. An imaging process according to claim 2 wherein said liquid having low volatility has a boiling point greater than about 250* F. 